Field of the Invention
The present invention relates to a toner for use in a recording method using electrophotography, or the like, an image forming apparatus provided with the toner, and an image forming method using the toner.
Description of the Related Art
An analog-to-digital transition, advanced recently in the field of printers and copiers, has resulted in excellent reproducibility of latent images and high resolution. At the same time, demand for reduction in size of, in particular, printers been growing strongly.
Printers have conventionally been used in a mode in which a printer is connected to a network and used for printing by a large number of users, but in recent years, it has been often required to install a personal computer (PC) and a printer on respective desks of the users so that printing is performed at hand. Accordingly, space-saving is required of printers and also printers reduced in size are strongly required.
Further, printers reduced in size also need to ensure high image quality and high stability with small variation in image in a long-term use. Accordingly, a printer can be effectively reduced in size by reducing the size of an image forming apparatus equipped with fixing means or developing means, which takes a significant volume of the printer.
Concerning an image forming method, a two-component development system or a mono-component development system is used in an image forming method for use in an image forming apparatus, but the mono-component development system is more suitable for size reduction. This is because members such as a carrier are not used. According to Japanese Patent Application Publication No. 2005-173484 and Japanese Patent Application Publication No. 2006-154093, an image forming apparatus using a mono-component development system can be reduced in size by reducing in the diameter size of a toner carrying member or by not using a toner supply member that is arranged in contact with the toner carrying member. However, problems specific to such image forming apparatuses tend to manifest strongly therein.
Examples of such problems include development ghosts associated with toner regulation defects on a toner carrying member. When the toner carrying member is reduced in diameter size or the toner supply member that is arranged in contact with the toner carrying member is not used, the replacement of toner on the toner carrying member becomes insufficient. As a result, the toner is overcharged and toner regulation defects are generated. Such toner regulation defects appear to be more significant when the flowability of the toner is decreased as a result of an external additive being embedded in the toner during a long-term durability use.
A cleaner-less system is also extremely effective as a means for reducing the size of an image forming apparatus. In most image forming apparatuses, the toner on an electrostatic latent image bearing member that remained in a transfer step (referred to hereinbelow as “untransferred toner”) is scraped off with a cleaning blade and recovered in a cleaner container. Meanwhile, in the cleaner-less system, the cleaning blade and cleaner container are not used, which can result in significant size reduction of the image forming apparatus.
However, specific problems are also inherent to the cleaner-less system.
For example, in a portion of the electrostatic latent image bearing member where the untransferred toner is present, charging is implemented insufficiently in the charging step and non-uniformity is likely to occur during the development, hence image density non-uniformity is induced. Further, the external additive, which has been freed from the toner, remains on the electrostatic latent image bearing member even after the transfer step and contaminates the charging member, thereby causing charging defects and the appearance of white spots in a solid image.
Measures have been taken against the abovementioned development ghosts, image density non-uniformity, and white spots to increase the flowability of the toner and reduce a toner attachment force.
For example, Japanese Patent Application Publication No. H06-301236 suggests a magnetic toner configured of a binder resin, a magnetic body, and an external additive, the magnetic toner being characterized in that a toner fine powder to which the external additive has been attached is subjected to surface modification treatment by a hot air current in a dispersed state, and the immobilization of the external additive, coverage of the magnetic body, and sphering of the toner fine powder are performed simultaneously and instantaneously.
As a result of performing the so-called heat sphering treatment in such a manner, improvement in image quality and image stability during a long-term use are actually exhibited. However, in terms of preventing the abovementioned development ghosts, image density non-uniformity, and white spots, there is still room for further investigation and improvement.